A review of the literature indicates that the recent consensus is that spondylolisthesis is an acquired anomaly. The cause appears to be either a single major trauma (which is very rare) or a series of minor traumata that result in stress fractures through the pars interarticulars or the pedicles of the vertebrae involved.

This study concerns 216 patients operated on consecutively. Spondylolisthesis was present at the lumbosacral level in 190 of them; between the fourth and fifth lumbar segments in nineteen; and between the third and fourth lumbar segments in seven. In only seven cases was the slipping greater than Grade 2. The procedure performed was spine fusion except for the Gill operations in twenty-five patients. Spine fusion was established by the Meyerding techisique, and a comparison is made between results achieved with iliac bone grafts and results obtained with tibial bone grafts. In only twelve patients were plaster casts used. All other patients were allowed to be up with a belt or corset within two weeks of the day of operation, and no other form of immobilization was used.

In this series, the best results were obtained for patients in whom iliac fusion was done with concurrent removal of loose dorsal elements. Iliac fusion was definitely more satisfactory, in respect to both clinical results and the percentage of successful fusion, than was tibial fusion. Removal of loose dorsal elements had no adverse effect on the number of instances of successful fusion and the procedure seemed to improve the clinical results to a significant degree.

In more than 60 per cent of the patients, exploration of the nerve roots was done at the time of operation, and in forty-six instances definite protrusion or extrusion of intervertebral dises was found. This is a higher incidence of this defect than is reported in most series of spondylolisthesis.